An industrial robot can be controlled with the aid of a joystick. During a teaching or programming procedure, the position and/or orientation of the robot tool can be controlled in the desired manner by means of the joystick. The joystick can either be arranged on a fixed control cabinet or on a smaller, separate programming unit, which during programming or teaching can be held in the hand or be placed on a table. In order that programming shall not take an unreasonably long time, it is necessary that a full deflection of the joystick causes a movement with a relatively high speed of response in the robot. During the teaching procedure it may be necessary for personnel to stay in the vicinity of the robot in order to eliminate the risks of injuries which arise in this connection, a safety plate is arranged on programming units of the above-mentioned kind, on which safety plate the operator's hand rests when operating the joystick with the aid of the fingers. When the hand is removed, the safety plate senses this and influences the control system such that the joystick is rendered inoperative. In this way, it is prevented that an unintentional contact with the joystick gives rise to a movement of the robot. A device of this kind is described in Swedish printed patent application 450 285 and in Asea Journal 1982, No. 6, pp. 145-150.
In the known device there may be a certain risk that the operator, in an emergency situation, reacts incorrectly and instead of removing his hand from the safety plate presses even harder, whereby the robot continues its movement with an ensuing risk of both material damage and personal injury. To avoid this it has been proposed to use a contact device, actuated by the safety device, with two end positions located on different sides of an operating position, one of the end positions constituting the initial position (the rest position) and the other end position an extra neutral position. A drawback with this design, however, is that the contact device while returning to the initial position has to pass the operating position, whereby the safety circuit is briefly closed with an ensuing risk of uncontrolled movements of the robot.